Builtins: control the use of pager from the command table.

This moves the built-in "always-use-pager" logic for log family
to the command dispatch table of git wrapper.  This makes it
easier to change the default use of pager, and has an added
benefit that we fork and exec the pager early before packs are
mmapped.

Pointed out by Juergen Ruehle <j.ruehle@bmiag.de>.

Signed-off-by: Junio C Hamano <junkio@cox.net>

builtin-log.c

@@ -34,7 +34,6 @@ static int cmd_log_walk(struct rev_info *rev)
 	struct commit *commit;
 
 	prepare_revision_walk(rev);
-	setup_pager();
 	while ((commit = get_revision(rev)) != NULL) {
 		log_tree_commit(rev, commit);
 		free(commit->buffer);

git.c

@@ -211,6 +211,7 @@ static int handle_alias(int *argcp, const char ***argv)
 const char git_version_string[] = GIT_VERSION;
 
 #define NEEDS_PREFIX 1
+#define USE_PAGER 2
 
 static void handle_internal_command(int argc, const char **argv, char **envp)
 {
@@ -218,13 +219,13 @@ static void handle_internal_command(int argc, const char **argv, char **envp)
 	static struct cmd_struct {
 		const char *cmd;
 		int (*fn)(int, const char **, const char *);
-		int prefix;
+		int option;
 	} commands[] = {
 		{ "version", cmd_version },
 		{ "help", cmd_help },
-		{ "log", cmd_log, NEEDS_PREFIX },
-		{ "whatchanged", cmd_whatchanged, NEEDS_PREFIX },
-		{ "show", cmd_show, NEEDS_PREFIX },
+		{ "log", cmd_log, NEEDS_PREFIX | USE_PAGER },
+		{ "whatchanged", cmd_whatchanged, NEEDS_PREFIX | USE_PAGER },
+		{ "show", cmd_show, NEEDS_PREFIX | USE_PAGER },
 		{ "push", cmd_push },
 		{ "format-patch", cmd_format_patch, NEEDS_PREFIX },
 		{ "count-objects", cmd_count_objects },
@@ -275,8 +276,10 @@ static void handle_internal_command(int argc, const char **argv, char **envp)
 			continue;
 
 		prefix = NULL;
-		if (p->prefix)
+		if (p->option & NEEDS_PREFIX)
 			prefix = setup_git_directory();
+		if (p->option & USE_PAGER)
+			setup_pager();
 		if (getenv("GIT_TRACE")) {
 			int i;
 			fprintf(stderr, "trace: built-in: git");